A VAD/SS system provides for voice activity detection (VAD) and silence suppression (SS). VAD provides for the detection of voice energy on a channel of a transmission pipe for an electrical communication system. Not detecting such voice energy may be considered as the detection of silence. Such silence may nevertheless be transmitted over such transmission pipes because of the automatic functioning of the communication system. Such transmission of silence is normally undesirable since it occupies the channel with the transmission of energy which does not convey useful information. Accordingly, it is desirable for such transmission of silence to be suppressed.
Such suppression of the transmission of silence is provided by the SS portion of the VAD/SS system. Silence Suppression further provides for the making of the channel, over which the silence has been suppressed, available for the transmission of active voice energy from other channels of the transmission pipe. This effectively blocks the transmission path between the original speakers/listeners provided by the channel. Also, this provides for a more efficient use of the transmission pipe by reducing the portion thereof which is carrying silence. Bandwidth savings, or compression, are thereby provided by allowing multiple connections to share the bandwidth of a large transmission pipe. Less overall bandwidth is required resulting in saving for the transmission service provider and transmission service customer.
The VAD/SS system may also provide a noise-matching process where the decoding end of the connection or channel supplies some noise during periods when the VAD has determined the absence of speech. The purpose of this supplied noise, also referred to as matching noise, is to mask the operation of the VAD/SS system on connections that contain noise in addition to the voice energy which is detected by the VAD. Such additional noise may be referred to as actual channel noise or background noise. On such connections the listener hears this actual channel noise when the other party is speaking. However, when that party stops speaking and the VAD determines that the connection is in a non-voice state, i.e., detects silence, the SS initiates silence suppression which makes the channel unavailable to the listener. As a result, the listener no longer hears the actual channel noise. These transitions between channel noise present and channel noise absent produce an unnatural sound that may raise concerns of the listener regarding the proper functioning of the communication link. Also, such concerns may be raised by the complete absence of audible sounds.
The unnatural sounds associated with the transitions between the presence and absence of the actual channel noise may be disguised to some extent by the addition of the matching noise. This improves the experience of the listener. The extent to which the transition is disguised depends upon the similarity between the actual channel noise, and the matching noise. Unfortunately, matching noise from known VAD/SS systems typically has a relatively constant frequency and decible level, and, thus has a relatively basic sound. Such matching noise may be sufficiently different from the actual channel noise, especially where this actual noise is dynamic, that the addition of the matching noise may result in an audible transition from the actual channel noise, and an unnatural sound.